The present invention relates to the production of polyphenols and, more specifically, to the production of polyphenols from aralkyl tertiary hydroperoxides.
In the production of aralkyl tertiary polyhydroperoxides such as for example p-diisopropylbenzene dihydroperoxide, there is also produced the corresponding monohydroperoxide. Indeed, the rate of formation of the monohydroperoxide is approximately proportional to the concentration of the aryl tertiary alkane in the reaction mixture and that of the dihydroperoxide to the concentration of the monohydroperoxide. The reaction, however, comes to a virtual standstill before all of the monohydroperoxide is converted to the dihydroperoxide and consequently for a given amount of the aryl tertiary alkane only a small proportion of the dihydroperoxide is obtained.
It is known that the oxidation reaction can be conducted so as to yield a considerably higher amount of the aralkyl tertiary dihydroperoxide if the dihydroperoxide is separated from the oxidation reaction mixture alternately or concurrently with the oxidation reaction while the oxidation is continued with the remaining reaction mixture. As a practical matter, in a continuous reaction, the dihydroperoxide is continuously removed from the reaction mixture and the remaining portion of the oxidation reaction product is recycled to the oxidation reaction to convert the large amounts of monohydroperoxide present in the recycle stream to dihydroperoxide.
Unfortunately, the oxidation reaction product from which the dihydroperoxide has been removed and which is recycled to the oxidation reaction, in addition to containing large amounts of the monohydroperoxide, also contains undesirable by-products and impurities which are quite detrimental to the efficiency of the oxidation reaction. For example, it is known that in such reactions keto aryl tertiary alkanols, aralkyl tertiary dialkanols and other by-products are also produced. These materials, particularly the keto aryl tertiary alkanols hinder the oxidation reaction. As a consequence of the above-described recycle of the substantially dihydroperoxide free oxidation reaction product to the oxidation reactor, these impurities and by-products continue to build up to the point where, it the oxidation reaction is to be conducted efficiently and economically, it may become necessary to completely discharge the reactor contents and charge the reactor with fresh reactants.
In co-pending application, Ser. No. 285,481, now abandoned, is described a process wherein the by-products, discussed above, which would normally build up in the reactor are purged from the system, preferably in a continuous manner, thereby maintaining the reactor in a substantially steady-state condition. Briefly the process involves taking a portion of the oxidation reaction product stream after removal of the greater part of the polyhydroperoxide and separating the substantially polyhydroperoxide free reaction product into at least two fractions, one of which contains most of the impurities and by-products which have a deliterious effect on the oxidation reaction. While the process described in the aforementioned co-pending application works remarkably well at maintaining the desired oxidation rate, certain problems are presented. For one, the fraction which contains the undesirable by-products and impurities also contains a significant amount of the monohydroperoxide. Such a condition poses a disposal problem which is, at best, economically undesirable and, at worst, dangerous, the monohydroperoxide being quite reactive and under certain conditions explosive. Moreover, the fraction containing the by-products also contains a small but economically significant amount of the polyhydroperoxide which, if recoverably, could be converted into the desired end product, the polyphenol. However, separation and recovery of the polyhydroperoxide from the by-product laden fraction is not economical.